1. Field of the Invention
Safety devices for vehicles to prevent the movement of the vehicle whenever the operator leaves a seat and opens the driver's door. The system employs an electrical circuit using respective seat and door switches in conjunction with control of the parking brake.
2. Background of the Invention
Safety systems for vehicles are sometimes known generally as "dead man controls" and are quite common not only for vehicles but also for machinery, lawn mowers, and in many other fields of invention. Basically, such devices employ a switch which is actuated whenever the operator performs a certain act, or fails to perform a certain act such as taking his hand off a control, leaving the seated position, or exceeding certain limits of operation. There is considerable prior art having to do with the operation of vehicles such as trains or automobiles. The present device is especially applicable to a dump truck as a precaution whenever the truck is parked so as to require that the parking brake be applied. The prior U.S. patents include the following:
U.S. Pat. No. 3,790,223 closes a vacuum brake control system including a solenoid which is energized to apply the vehicle's brakes when both seat and door switches (in series) sense that the vehicle's operator has opened the door and left his seat;
U.S. Pat. No. 2,734,590 discloses an automatic brake setting and releasing device which senses both the presence of an operator and the condition of the vehicle's door;
U.S. Pat. No. 3,190,223 discloses a brake control system including a solenoid which is energized to apply a vehicle's brakes when seat and door switches sense the vehicles's operator has opened the door and left the seat;
U.S. Pat. No. 3,830,330 discloses an automatic parking or emergency brake system including switches which sense pressure on an operator's seat and other devices such as the throttle;
U.S. Pat. No. 3,721,310 discloses a safety brake system which applies an emergency brake in response to opening of the vehicle door when the ignition switch is off or while the gear selector is in the neutral position;
U.S. Pat. No. 4,655,313 discloses a vehicle seat switch for sensing the presence of a vehicle's operator; and
U.S. Pat. No. 4,838,617 discloses a braking system for applying the brakes to a vehicle when switches sense the opening of a door.
None of the above noted patents disclose a particular simple system presented in this description of a preferred embodiment wherein the parking brake is automatically applied whenever the operator leaves the seat and opens the door. Furthermore, the present system does not require the use of electrical relays which necessarily include spring biased switch mechanisms that sometimes are not dependable but the present system uses an arrangement of electrical switches which control the current in the system efficiently, inexpensively and effectively to operate the system through the use of a seat switch and a door switch electrically wired from a battery to the electric solenoid for the automatic operation of the spring brake air valve of the parking brake. This provides a simple and dependable system which is virtually fool proof and is practically impervious to dirt and corrosion and other conditions which develop throughout the use of utility trucks, such as a dump truck.
A principal advantage of the present system is the simplicity and economy of use and installation together with dependability of operation.